Certain properties of gypsum (calcium sulfate dehydrate) make it popular for use in building products. Typically, gypsum is employed in panels or boards known as wallboard, a commonly used building material for a variety of structures. These gypsum products are produced by mixing anhydrous calcium sulfate or calcium sulfate hemihydrate with water and allowing the mixture to hydrate or set as calcium sulfate dihydrate, a relatively hard material. In the form of wallboard, there is a core panel of set gypsum sandwiched between a pair of liners made of paper or glass fiber although any type of sheet-like material could be used.
In many applications, wallboard is exposed to moisture and water which presents a problem in that set gypsum readily absorbs water and loses its strength. A variety of techniques have been used to render gypsum wallboard water-resistant or water-repellant.
Many attempts have been made in the past to improve the water resistance of gypsum products. These attempts have included the incorporation of water-resistant materials such as metallic soaps, asphalt, waxes, silicon compounds, synthetic polymer resins, or synthetic polymer emulsions within the gypsum slurry during the manufacturing process. They have also included attempts to coat the finished gypsum product with water-resistant films or coatings.
There are many additives cited in the patent literature which claim to improve moisture resistance. These additives include, for example, vegetable oils, fatty acids, wax emulsions, styrene butadiene emulsions, vinyl acetate emulsions, asphaltic emulsions, siliconized waxes, polysiloxanes, polyurethanes, and polyvinyl alcohol.
The present invention relates to resin dispersions that improve the moisture resistance of gypsum structural products used in industrial, commercial or residential applications where water and humid conditions are encountered.